Posted by: magmatist | October 17, 2011

MBVRC begins new Baker monitoring program

models for hydrothermal system at Sulphur Springs, Mount Baker

MBVRC has begun sampling water from a spring at 3400′ near Schreibers Meadow. Water chemistry at the spring indicates that the water contains traces of magmatic chemical influence, meaning it has a connection at depth with magma or with fluids and gases coming off magma. We hope to eventually train ‘citizen scientists’ to assist with this work. Currently all 5 MBVRC board members are getting experienced with the methods.

Robert H. Mariner and William C. Evans of the USGS identified the Sulphur Spring site as the single best hydrothermal-monitoring site at Mount Baker because of its chloride content and magmatic-carbon signature.  Two post-2000 Sulphur Creek water samples showed 90% magmatic (dead) carbon, with carbon-isotope composition similar to Mount Baker fumaroles; chloride concentration ranges from 4.8-6.2 mg/L (~ 0.0005 – 0.0006 weight %) so it’s a tiny signal.  Still, it’s at least an order of magnitude higher than the Cl concentration in precipitation. These chemical concepts are explained a bit more at the bottom of this post*.

This active monitoring site is near the Schriebers Meadow cinder cone, the source of the ca. 8,800 14C years BP Sulphur Creek lava flow. Monitoring is done as a volunteer effort under the auspices of hydrogeologist Steve Ingebritsen and geochemist William Evans at the USGS in Menlo Park, California. This is part of a larger project to measure and monitor hydrothermal systems throughout the Cascade Range. More information on this USGS project is available at the USGS ‘Dynamics of hydrothermal systems website. The website also has links to databases of geothermal and hydrothermal data, and a host of other volcano-related information and monitoring projects. There is also a volcano-hydrothermal monitoring methods website.

Monitoring the spring’s chemistry is a way to track changes in the magmatic and hydrothermal system beneath Mount Baker. Collecting fumarole gases at Sherman Crater is a related but much more arduous method to do the same thing. The location of the spring in Schreibers Meadow will allow MBVRC to collect data for USGS much more frequently; ideally monthly for a year or so. Access to the area in the winter will likely require coordination with volunteers with snowmobiles (the sample site is in a heavily used snowmobile recreation site).

Sue Madsen, Doug McKeever, and Pete Stelling gage the stream below Sulphur Springs.

It is not sufficient to collect water samples. The stream must also be gaged during each sampling visit in order to calculate flow volumes. Gaging involves measuring the depth and flow velocity across the entire width of the stream, in order to calculate concentrations of the various chemical species, such Cl, SO4, and He. Alkalinity and pH of the water are also measured.

Boulder Creek, which drains Sherman crater, is another obvious monitoring target but lacks a deep thermal (i.e. chloride) signature.  Further, monitoring at Boulder Creek is hampered by its shifting alluvial stream channel and rapid current.  Part of MBVRC’s responsibilities on this project will be to search out a safe place to cross the creek in order to gage the flow.

*Basic chemistry concepts:

‘Dead carbon’ has no detectable trace of the isotope C14. It takes 50,000 years for the radioactive C14 isotope to decay to such a vanishingly small level. Absence of C14 in ground waters indicates that the water been isolated from the atmosphere (source of C14) for that period of time.

Chlorine is a very tiny proportion of atmospheric gas, though it is a significant component in the crust, where it reaches around 126 ppm (parts per million). Cl dissolves readily in magma, where it is concentrated. Chlorine concentrations at Sulphur Springs are quite elevated relative to precipitation in the area which typically contains 10 times less Cl.

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